1. Field of the Invention
The present invention relates to an inkjet printer head that ejects ink droplets through nozzles onto a recording medium to form images thereon.
2. Related Art
FIG. 1 shows a configuration of a conventional inkjet head 101, which is formed with a nozzle 110, a common ink chamber 102, a pressure chamber 103, and a restrictor 106. The pressure chamber 103 is in fluid communication with the nozzle 110 and also with the common ink chamber 102 via the restrictor 106. A diaphragm 104 defines an upper wall of the pressure chamber 103. A piezoelectric element 105 is attached onto the diaphragm 104 for deforming the same. A filter 107 is provided inside the common ink chamber 102 for preventing any foreign materials from entering the pressure chamber 103 and from blocking the nozzle 110.
In this configuration, when a driving voltage is applied, the piezoelectric element 105 changes an internal pressure of the pressure chamber 103 and ejects an ink droplet through the nozzle 110. More specifically, a rising edge of the driving pulse deforms the diaphragm 104 in a direction to increase the volume of the pressure chamber 103, thereby generating a negative pressure in the pressure chamber 103. This negative pressure draws ink from a manifold (not shown) into the pressure chamber 103 through the common ink chamber 102 and the restrictor 106. Then, a lowering edge of the driving pulse releases the deformation of the diaphragm 104 to decrease the volume of the pressure chamber 103 to its initial volume. This increases the internal pressure of the pressure chamber 103 and ejects an ink droplet through the nozzle 110.
There has been increasing demand for an inkjet head that can be driven at a high frequency to eject ink in order to realize an inkjet printer capable of high-speed high-quality printing. One method for increasing the driving frequency is to increase a Helmholtz resonant frequency, which is determined by a dimension of the inkjet head 101 and the like.
Also, Japanese Patent-Application Publication No. HEI-08-290571 has proposed an inkjet head where:
0.5 less than Mn/(Mn+Ms) 
wherein Mn is an inertance of a nozzle; and
Ms is an inertance of a restrictor.
By setting the relationship between the nozzle and the restrictor in this manner, it is possible to eject spherical ink droplets regardless of high driving frequency.
However, mere the above relationship between the inertance of the nozzle and that of the restrictor does not solve the following problems. That is, when the pulse width of the driving pulse, i.e., the time duration from when the pressure chamber volume is increased until when the increased volume is reduced to its initial volume, is shortened in order to increase the driving frequency, only insufficient amount of ink may be drawn into the pressure chamber before ejecting the ink droplet due to delay in ink introduction by means of inertial, causing improper ink ejection. On the other hand, elongating the driving pulse width in order to introduce sufficient amount of ink into the pressure chamber sacrifices a frequency respond time. Moreover, high-frequency driving adversely increases the residual pressure vibration of a meniscus, which in turn fluctuates ink ejection speed. In worse cases, ink will not be ejected.
It is an object of the present invention to overcome the above problems and also to provide an inkjet head capable of performing stable ink ejection at a high frequency.
In order to achieve the above and other objects, there is provided an inkjet head including a body and a diaphragm. The body is formed with a nozzle, a pressure chamber in a fluid communication with the nozzle, a plurality of restrictors, and a common ink chamber. The common ink chamber supplies an ink to the pressure chamber via the restrictors. The diaphragm defines a wall of the pressure chamber. Each restrictor has an opening facing to the diaphragm.
There is also provided an inkjet head including a body and a diaphragm. The body is formed with a nozzle, a pressure chamber in a fluid communication with the nozzle, a plurality of restrictors, and a common ink chamber. The common ink chamber supplies an ink to the pressure chamber via the restrictors. The diaphragm defines a wall of the pressure chamber. The body includes a restrictor plate formed with the plurality of restrictors. The restrictor plate faces to the diaphragm.
Further, there is provided an inkjet printer including an inkjet head. The inkjet head includes a body and a diaphragm. The body is formed with a nozzle, a pressure chamber in a fluid communication with the nozzle, a plurality of restrictors, and a common ink chamber. The common ink chamber supplies an ink to the pressure chamber via the restrictors. The diaphragm defines a wall of the pressure chamber. Each restrictor has an opening facing to the diaphragm.